Telephone system



Dec. 10, 1,940. o; A. PEARCE TELEPHONE SYSTEM Filed Dec. 8, 1937 2 Sheets-Sheet l ATTY Dec. 10, 1940, l o. A. PEARCE 2,224,692

TELEPHONE SYSTEM Filed Dec. 8, 1937 A 2 Sheets-Sheet 2 INVENTOR i j- OWEN ,4V/5 PEARCE v ATTY.

Patented Dec. 10, 1940 PATENT OFFICE 2,224,692 TELEPHONE SYSTEM Owen Avis Pearce, Barnston, England, assigner to Associated Telephone & Telegraph Company, Chicago, Ill., a corporation of Delaware Application ,December 8, 1937, Serial No. 178,662

In Great Britain January 19, 1937 Claims.

The present invention relates to telephone or like systems and is more particularly concerned with finder switch arrangements for use therein for connecting a calling subscribers line to a 5 first numerical switch. The chief object of the invention is to provide an economical and emcient allotting scheme which can be applied with advantage in all types of finder switch systems and which obviates the need for separate rotary switches for allotting purposes.

According to one feature of theinvention in a telephone system employing iinder switches for connecting a calling line to a first numerical switch a variable number of iinders are adapted to operate simultaneously under the control of a start relay connected in a bridge circuit.

According to another feature of the invention in a telephone system employing finder switches for connecting a calling line to a first numerical switch finder switches are allotted for use under the control of a single set of common equipment adapted to allot a plurality of finders successively at intervals which are small compared with the time required for a iinder to complete its operation.

A further feature of the invention is that in a telephone system employing nder switches for connecting a calling line to a first numerical switch a 'finder is allotted for use in response to a momentary start impulse transmittedthereto from common equipment which is adapted to transmit an impulse to a further finder before that originally started has completed its operation in the event of simultaneous calls in a group.

The invention will be' better understood from the following description of one method of carrying it into eiiect, reference being had to the accompanying drawings comprising Figs. 1 and 2. These should be arranged side by side to form a circuit diagram of a portion of a finder switch system in which the switch mechanisms employed are all assumed to be of the longitudinal and rotary type disclosed in the application of Robert N. Saxby, Serial No. 54,287, led December 13, 1935. The general principles of the. system follow those described in Taylor Patent No. 1,914,540 of June 20, 1933, whereby primary line finders are arranged so that those iii'st taken into use (rst choice finders) are directly connected to first group selectors while those last taken into use (last choice finders) are arranged to be connected to first group selectors in a common group over secondary finder switches. The primary and secondary start and control sets and associated allotter switches which are normally provided in systems of this type have been replaced by so-called primary and secondary start relay sets, each comprising two relays only. Each individual finder switch is provided with all the necessary relays for setting and control purposes, 5 contacts of one relay in each switch being also utilised in connection witha'chain circuit allotting arrangement. The necessary changes of connection according to the conditions under which the finders are to be used are all made at 10 the intermediate distributing frame DF, no strapping changes having to be made internally. Thus the circle and dash connections shown are suitable for first choice primary finders which are directly connected to first selectors and also for secondary finders which are assumed to be identical with the primary finders while the dotted connections apply to last choice primary finders which are connected with iirst selectors by way of the secondary finders.

Considering now the circuit operation, when vthe subscriber whose line circuit is shown removes his receiver, the loop placed across the incoming speaking leads operates relay L. Thereupon armature ll disconnects the winding of relay K from the P lead extending to the final selector bank multiple and applies a busying earth thereto, while'armature Z2 and Z3 mark the position of the calling line in the rotary and vertical bank multiples respectively of the line linders serving the particularZOO-line group involved, it being understood that the upper and lower sets of contacts on the vertical bank extend individually to common leads VBA and VTBB respectively which are each common to a level of twenty subl' scribers. At the same time armature Z4 connects battery over resistance YA, which is common to the twenty subscribers on the calling level, to the primary start leads PSL which is common to the group of 200 subscribers. The common start relay-PS is thereupon yoperated and at its armature psl completes an energising circuit for relay SR which is slow both to operate and release. Assuming that none of the other line finders serving the group in question is at present in use, earth is also extended during the operating timeof relay SR over armature srl to operate relay A in the finder kcircuit shownwhich represents the first finder in the chain allotting circuit.

Relay A upon operating, at armaturea completesa locking circuit for itself in series with the lower winding of relay B which however cannot yet operate since it is short-circuited by the earth exten-ded from the start relay set. On the operation of relay SR after a short period, it opens its 55 own energising circuit at armature sr2 but due to its slug it does not release until a further short interval has elapsed. During this time the earth shunt is removed from the winding of relay B which now operates in series with relay A which remains held and thereupon armature b2 connects battery through resistance YB, which is individual to the finder switch, to common lead X extending to the bridge circuit in the start relay set. Since it is arranged that resistances YA and YB are equal and resistances YC and YD are also equal, the bridge will now be balanced and noy current will ow through relayr PS which therefore releases. relay SR there will be no earth to re-energise it and it will then remain normal. Relay B also at armature b4 extends the finder start lead over lead I I to the second nder in the chain in preparation for further calls, while at armature b3 it completes a self-interrupted driving circuit for the iinder vertical magnet VM from earth over armatures vtI and a3, contacts NPI and NRI, armatures b3 and a2, vertical magnet interrupter contacts om, magnet VM to battery.

Accordingly the wipers of the finder are raised step-by-step until the vertical wiper VW encounters the level marking battery via resistance YE whereupon relay VT quickly operates and at armature 'Utl disconnects the magnet driving circuit and at the same armature opens the holding circuit of relay A, relay B now being maintained operated Vover its upper winding. Meanwhile on the first vertical step of the finder the off -normal springs were mechanically-operated and at contacts N2 served to prepare a circuit for the rotary magnet RM and at contacts N3 to maintain Ia chain circuit to the second finder. On release of relay A after its slow period a self-interrupted driving ,circuit is completed for the rotary magnet RM from an earth which is connected to common lead I0 by Way of delayed alarm equipment which gives an alarm if the magnet remains .energised for more than a predetermined period,

Aare rotated in search of the calling line. On the first rotary step the rotary off-normal springs are Vmechanically operated and since the finder taken into use is a first choice finder battery through resistance YF is connected over armature b9, ro-

tary off-normal contacts NR4 and I. D. F. cross connection to the positive line of the group selector whereupon the A and B relays therein are operated and return a guard earth over the P conductor.

When the calling line is found, a circuit is completed to lock the rotary magnet RM which holds its armature in the operated position and thus arrests the motion, this circuit extending from earth, armature b1, rectifier MRA or MRB in a conductive direction, left-hand low resistance winding of either relay HA or HB, wiper and bank MI or M2 in accordance with the bank on which the calling line is situated, armature l2 of the calling relay L, the calling level on the lower section of the vertical bank, vertical wiper VW, armature bl, rotary magnet interrupter contacts rm in the operated position to battery via the magnet RM.

Assuming that the marking is on the MI bank, relay HA is operated in this circuit and at armawinding in series with the rotary magnet which Thus on the subsequent release of now releases, at armatures haI, haZ and ha3 eX- tends the rst set of negative, positive and private wipers through to the iirst selector, at armature had disconnects any circuit for relay HB and at armature haB extends earth from the P conductor to short-circuit the upper winding of relay B thereby bringing about its release. Relay B thereupon at armature bI opens a further point in the rotary magnet locking circuit, at armature b2 disconnects the resistance battery YB from the bridge circuit and at armature b8 opens the circuit of relay VT which releases. During this time the extension of the P conductor through from the first selector will have brought about the'operation of the calling subscribers cut-oit relay K from the guard earth and this relay releases relay L and connects earth to the subscribers meter MTR in readiness for metering. The release of relay L removes the vertical and rotary markings and disconnects the resistance battery' YA from the PSL lead. Relay PS will therefore remain normal until another call is originated since it is arranged that the removal of the resistance battery YB from the X lead on release of relay B takes place at approximately the same instant as relay L releases.

If the calling party had been connected to the M2 bank, relay HB would have been operated to switch through the second set of wipers, while if two calling lines are encountered in the samel position the rst of the relays HA and HB to operate will disconnect the circuit of the other one.

If two or more subscribers in any group originate calls at the same time, one line'nder will be started up for each level calling. Should, for

example, three subscribers on different levels originate calls simultaneously, then three resistvance batteries will be connected in parallel to the start lead PSL. Hence on the operation of relay B in the first finder selected, the PS bridge'will remain unbalancedl and relay PS will remain operated. Relay SR on releasing will therefore have `its circuit again completed and the second nder -in the chain will therefore be started up. The cycle of operations will in this case continue until three nders have been started up whereupon the three resistance batteries connected in parallel Ito the X'lead via the armatures of the B relays in the three finders concerned will balance the bridge and release relay PS. Thus it will be appreciated that if calls should be originated by subscribers on as many as ten different levels of the finders at any one time, a corresponding number of finders would be started off'at intervals of the order of fty milli-seconds only, the intervals representing the approximate time for relay SR to operate and release. If however, two or vmore subscribers on the same level call together,

one nder only will be started oft as is the usual practice. Immediately this nder switches through to one of the calling subscribers, a second finder will be started off and so on until all the calling parties have been connectedl through to first'selectors. The same considerations apply to the starting up of secondary finders by last choice primary nders when the latter are brought into use in a manner now to be described.

When all the first choice finders have been taken into use, the chain allotting circuit extends naturally to the rst of the last choice finders serving the group. As previously mentioned the last choice finders of each group of subscribers in the exchange are not directly connected to selectors but are connected by way of secondary cov nders to a common group of rst selectors. The secondary finder starting vand chain allotting arrangements are identical with thosey provided for the primary finders and thus itwill be appreciated that the last choice finders operate with respect to the secondary ndersin the same way as calling line circuits with respect to the primary finders. The secondary finders are assumed to be of the 200-line type so that for exchange maintenance purposes they are interchangeable with the primary finders. A-circuit diagram of a secondary finder has therefore not been shown since it is identical with the primary iinder indicated and its outgoing leads are connected over the I. D. F. to a group selector in the same manner as those of a first choice primary finder.

Considering now the circuit operation, when relay PS is again operated on the origination of a further call, the rst last choice nder inthe allotting chain circuit is started up and it thereupon functions in the normal manner until it cuts into the marked level and commences to hunt in a rotary direction. The rotary off-normal springs now at contacts NR2 and NRS oomplete corinections over the I. D. F. cross connecting leads to mark the position of the calling last choice finder in the vertical and rotary bank multiples respectively of the secondary iinder switches, while the resistance battery YG which is similar to the level marking battery YH in that it is common to the twenty last choice finders on the calling level of the secondary finders is connected o-ver the I. D. F. by way of armatures a2 and b3 and contacts NRI to the common secondary start lead SSL serving the group of 200 last choice finders. Relay SS in the secondary finder start group is thereupon operated and in the same way as relay PS it starts up the first secondary finder in the chain to search for the calling last choice primary iinder. In the meantime the latter continues its search for the calling line and when it is found either relay HA or relay HB is operated and switches the calling line through to the outgoing leads. No earth will be extended over the P conductor ho-wever to operate the calling subscribers cutoff relay K and to short-circuit relay B until the secondary iinder finds the calling last choice finder. When the secondary finder nds the marked position, relay HA or HB therein operates whereupon the calling line circuit is switched right through the primary and secondary nders to the group selector connected to the latter whereupon earth will be extended back to shunt down the B relays in both the nders and at the same time to operate the cut-oit relay K. All vertical and rotary markings in the two iinder banks are now removed and the potentials applied to the common leads PSL, X, SSL and Y are disconnected in preparation for a further call.

When the complete train of automatic switches has been set up and the wanted party replies, a booster battery metering pulse is extended back along the P conductor and this feeds through rectifier MRA or MRB according to whether relay HA or HB has been operated, and it operates the calling partys meter MTR over either the MI or the M2 lead in well-known manner.

On the release of the connection at the end of conversation, earth is removed from the P conductor by the controlling switch in the train thereby releasing the operated switching relay in the nder or finders brought into use and also relay K in the calling subscribers line circuit. A self-interrupted driving circuit is now completed for the rotary magnet in the finder or finders as the case kmay be from the release alarm conductor I0, so that the wipers are rotated clear of the banks after which they fall vertically and restore below the banks to the normal position where the driving magnet circuit is opened at` the ofi-normal contacts N2. The oit-normal contacts N3 then re-connect the chain allotting lead to the iinder so that if there are no other earlier finders in the chain which are also free for use, this iinder4 will be taken into use on the origination of another call.

Should the calling party restore his receiver before the finder taken into use has completed its vertical movement, the vertical and rotary bank markings will be removed but since relays .A and B remain locked jthe finder will continue to step vertically until it reaches the 10th level. On this level the normal post springs NP are mechanically operatedtby the switch shaft and at contacts NPI complete a locking circuit for the vertical magnet VM via the current limiting resistance YJ and at the same time open the series holding circuit of relays A and B. If there is a battery marking potential provided on this level by another calling subscriber, relay VT will operate and the switch will cut in and search in a rotary direction in a normal manner. If however no marking is encountered, relay VT will not be operated and the vertical magnet will remain locked until relay A releases when the switch will cut in, rotate its wipers clear of the banks, and restore to normal, no testing taking place during rotation since relay B is normal and no earth is therefore supplied to relays HA and HB. If the calling party should hang up during the rotary motion the finder will merely continue to rotate until the wipers are clear of the banks and will then restore.

If the rst group selector associated with a primary finder is artificially busied for testing purposes by the connection of earth to the P conductor, relay B in the primary iinder is perated over its upper winding, thereupon preupper set of test jack springs to the lower set'Y so that the chain allotting circuit is extended through to the next switch in the chain.

I claim:

1. In a telephone system, lines, rst numerical switches, iinder switches having access to said lines, a start relay connected in a balanced bridge circuit and controlled from calling ones of said lines to cause a variable number of said finders to operate simultaneously to connect calling lines to said numerical switches, said bridge circuit balanced whenever there are as many finders started as there are lines calling. y

2. In a telephone system, lines, iinder switches having access to said lines for extending connections therefrom, a common equipment responsive to a call from one of said lines to transmit a momentary start impulse to one of said nders to cause said nder to find said calling line, said common equipment operated responsive to a second call from one of said lines to transmit a start impulse to a second one of said nders before the iirst calling line.

switch, a relay in each finder switch slow to operate and slow to release, said relay having means for breaking its own circuit and also having means for cutting ofi the start impulse to the finder switch.

4. In a telephone system, lines, finder switches having access thereto, a start relaycommon to said lines, a chain start circuit, means responsive to a call from `one of said lines for establishing a `calling position to operate said start relay to transmit a momentary impulse over said start circuit to start one of said finders to find the calling line, means responsive to the operation of the nder vto extend the start circuit to the next available finder switch, the calling condition in said line being maintained until the line is seized by a starting finder, and means for neutralizing said calling condition in the starting circuit to insure starting only as many finders as there are lines simultaneously calling.

5. In a telephone system, a group of lines divided into sub-groups, a group of nder switches having access to said lines, a start relay common to said lines and responsive to calls from said lines vto cause the simultaneous operation of a plurality of nder switches to hunt for calling lines, a bridge circuit for said start relay, a branch of said bridge circuit for each sub-group of lines including a battery feed through a resist-ance, another branch circuit including a battery feed through a resistance for each iinder switch inoperation, said bridge circuit balancing and preventing the starting of more nders when the number of calling sub-groups equalize the nurnbers-of iinders in operation.

OWEN A. PEARCE. 

